Thermoxerography



Dec. 15, 1964 CURME 3,161,529

THERMOXEROGRAPHY Filed March 24. 1961 HE M? Y 6. CURME IN V EN TOR.

ATTORNEYS United States Patent EJQELSZ? Henry G. (Insane, Rochester, NSEL, assignor to Eastman Kodak Qompany, Rochester, N.Y., a corporation of New Jersey Filed Mar. 24, 1961, Scr. No. 93,957 9 flaims. (Cl. 117-475) This invention relates to xerographic printing.

One unusual feature of the invention is the use of heat to produce the imagewise distribution of conductivity necessary for the imagewi e formation of an electrostatic charge image. Processes and apparatus employed in thermography are applicable to the making of the thermal image which in the present invention is converted to an image in terms of electrical conductivity or resistivity.

A second unusual feature of the present invention is the inverse effect (i.e. an increase in effective resistivity) due to the exposing energy. The present invention can use the heat from radiant energy either by converting it to thermal energy, for example by absorption in the characters printed on a document or by heating the recording layer directly by radiation. This second unusual feature of the invention is the increase in the ability of the recording material to store electric charge (which is usually considered as an increase in resistance) due to the heat, whereas the simplest forms of xerography decrease this ability (or resistance) of the recording medium by exposure to light. This change in the ability to store charge is believed to be (but need not be) associated with a change in electrical resistance.

The present invention can be combined with the pro duction of multiple prints from a matrix which has been exposed and charged only once or with transfer printing by inverse transfer of toner. Also a toned matrix after such multiple printing may be cleaned, recharged and re printed without additional exposure.

Cross reference is made to a copeuding application Serial No. 118,593, filed lune 21, 1961, by W. J. Dulmadge and W. A. Light having to do with a thermoxerographic process in which the heat creates an increase in conductivity rather than an increase in resistance.

In the present invention the electrostatic charge is applied after the exposing rather than before since prior to exposure, the whole layer is relatively highly conducting and will not store a charge. Since the thermographic exposure takes place first and the xerographic charging and toning takes place afterwards, the process may be referred to as thcrmoxerograph as distin uished from xerothermography described in copending applications Serial No. 25,108, iarvis, and Serial No. 25,109, Dulrnadge and Jarvis, both filed April 27, 1960.

The object of the present invention is to produce an inexpensive record. This is possible since the thermally sensitive layers employed can be produced relatively inexpensively. It is also an object of the invention to produce a high quality, high contrast, high resolution print.

The invention may employ various alternative systems to provide the increase in resistance on heating. Some of the simpler satisfactory embodiments merely drive out the moisture locally which provides a layer in which the resistivity image is not permanent but remains for considerable time to allow charging and developing. Another relatively simple embodiment employs layers containing electrically conducting solvents which are driven out by the heat and the resistivity images are again semi-permanent but presist long enough to excellent prints. The most permanent resistivity images which have bee employed in the present invention are those in which there is a chemical change, for example a cross linking between molecules, of the layer so that'it becomes relatively nonconducting where heated and remains conducting for a very long period of time, several months or even years, in the unexposed areas.

There are also some simpler embodiments of the invention in which the conducting layer contains an ionic salt which is thermally unstable and which reverts to a nonionic material when heated. One very practical embodiment of such a system employs the ammonium salt of carboxylic acid.

And still another embodiment of the invention employs a resin which is coated with interstices or gaps in the structure which allows some conductivity. Upon heating, the resin fuzes together and a continuous film is produced which is insulating. As examples of this, latex coated from an aqueous solution and discontinuous wax coatings have been used.

When the final print is made on the layer which is heated in contact with an original document, the print is laterally inverted and it is customary in some cases to use transparent sheeting when making such a record since the print can then be viewed through the sheeting itself. The transfer embodiments, in which the developer, toner or ink is transferred to or from a third sheet does not have lateral inversion in the final print and hence for many purposes is preferable; the sensitive sheet need not be transparen in the transfer embodiments.

A special or unusual application of the present invention is observed in connection with the direct heating of silver images in gelatin carried on a paper or film base. The same effect would occur with a carbon image in polyvinyl alcohol. These silver-gelatin systems are of less practical significance than the main embodiments of the invention, but are mentioned as an aid in the understanding of the operation of the invention. In these special cases, heat absorbed by the silver and thus conducted to the adjacent gelatin, dessicates the gelatin causing it to have relatively hi h resistance, at least temporarily. The surface is then charged and the charges are retained only adjacent to the silver image since the more moist gelatin in the non-silver areas is sufficiently con ducting that it does not store the charge. This electrostatic image is then toned by any of the usual xerographic methods and thus we have a toner image on the original document itself, which is a little unusual of course. The toner serves to intensify the document image or, more usually, it is transferred to another sheet as a positive of the document. This positive reproduction is right-reading only if the heated document is wrong-readin when viewed from the gelatin side, and right-reading when viewed through the base. Autopositive film is useful for producing prints in this manner since it is positive and is right-reading viewed through the base when exposed with the gelatin side facing the lens of the camera.

Other objects and advantages of the invention will be understood from the following description when read in connection with the accompanying drawing and from the specific examples also given below. In the accompanying drawings:

FIG. 1 schematically illustrates one embodiment of the invention.

FIG. 2 similarly illustrates a slight modification of the system shown in FIG. 1.

PEG. 3 similarly illustrates the transfer printing from a toner image produced on an original positive print.

In EEG. i a thermal exposing apparatus of standard type is illustrated for convenience, but the present inven tion may use any system for providing the thermal exposure. A recording sheet ill placed in contact with a document 1 to be copied is passed through the entrance slot 33 of a thermal exposing machine and passes over drum M. The sandwich of the two sheets is held in contact with the drum idby a belt 16 illustrated schematically and as the sandwich passes over the drum 14 the heat absorbing characters on the document ll receive radiant energy from a heat lamp 1% and by direct conduction the adjacent areas of the sheet 1b are heated. In this embodiment the sheet in is a transparent one. According to the invention, the localized heating of the layer, adjacent to the characters on the document ll; cause the layer to become effectively non-conducting. Prior to such exposure the layer it? is sufiiciently conducting that it will not hold an electrostatic charge.

After exposure the layer may be charged by any suitable means such as a corona wire 29 which is held at high potential relative to a backing roller 21 by means of a source of potential indicat schematically at 22. Thus the surface of the sheet it? which was in contact with the document 11 receives the charge. This charge remains on the insulating areas but is qui kly dissipated in the non-heated areas of the layer ltl. Any of the usual means for developing electrostatic images may then be used to apply toner to the patternwise charged surface. In FIG. 1 a magnetic brush 39 held at positive potential by a source indicated schematically at 33, applies powdered toner to the charged areas as the sheet 13* passes between the magnetic brush and a grounded backing roller 32. Thus a toner image Ed is produced on the undersurface of the transparent sheet it), and in order to be right-reading it must be viewed by the eye or" an o server through the sheet ltl. The magnetic brush 3% need not be at a different potential from the backing roller 32.. Both are usually grounded or the brush 3d may be at a potential slightly lower than that of the backing roller, to insure clear background areas in the toned image.

The charging step may provide either a positive or negative charge and, as is well known in xerography the I than it does in the unheated state. The recording sheet must transmit infrared, whether or not it is also transparent to visible light. The ability to hold charge may be either a permanent one or a temporary one, but if it is temporary the charging and toning must be applied during the time when a charge is stored in the heated areas.

The toner image 35 may be transferred by pressure to a receiving sheet or" paper. In this case the final print is right-reading. The heat sensitive sheet ill need not be transparent and if the change in resistivity with heat is more or less permanent, the sheet may be recharged and re rinted many times as in xeroprintin Also (and this is one of the important applications of the present invention) multiple prints may be made by the inverse transfer system. The number of prints so obtainable depends on the intensity of the charge (measured in volts) which can be held by the resistivity image and this in turn depends on how high a resistance is produced by the heatin 7 In FIG. 2 the sheet 4d, which need not be transparent in this case, is charged on the surface opposite to that which was in contact with the document during the thermal radiation step. The resolution is not quite as good in this case as in the arrangement shown in H6. 1 since the surface to be charged is separated from the document by the thickness of the layer ll? itself. On the other hand, the syst m shown in FIG. 2 has the advantage that when the toner S1 is applied to the upper surface of the sheet In FIG. 3 an ordinary direct positive transparency is used, consisting of a gelatin layer 51 containing a silver image 52 and car led on a transparent support St. The support need not be transparent and could be of paper. The heating of the silver image 52 by radiation from a lamp 53 is indicated schematically but could just as easily be performed in a standard thermal exposing machine such as that illustrated in FIG. 1. Thus an ordinary transparency (without any separate heat sensitive sheet) is heats The radiation from the high intensity lamp 53 absorbed by the silver 52 heats the adjacent areas of the gelatin 5i and it also heats the adjacent areas of the supporting film 5% We are here concerned with the heating of the gelatin. This heating of the gelatin desiccates it to the point that it has the ability to store charge received from a corona. wire 2% whereas the areas or the gelatin which have not been so heated i.e. in the absence of silver will not store a charge. The film itself is then passed under a magnetic toning brush 3 and toner is applied to the areas adacent to the sliver image 52. This toner image serves to intensify the silver image 52. Alternatively this toner iage may be transferred, as shown in FIG. 3 to a receiving sheet as by pressure contact illustrated by a roller 62. The toner image 65 carried on the undersuriace of the sheet 61 may be viewed directly by an observer whose eye is located at 6%. The image will be right-reading providing the silver image 52 is right-reading when viewed through the base 58. This is the usual case when the autopositive film is exposed in a camerawith the emulsion side facing the lens. Since the effect in the case of a gelatin layer is due primarily to driving out of moisture, and since ordinary gelatin tends to reabsorb water from the atmosphere very rapidly, the best quality, highest contrast, prints are obtained when the charging and toning steps follow the heating step very quickly. Thetransfer step may be delayed, of course. The example involves the driving out of water from a gelatin layer containing a silver image. The same eifect would be obtained by driving out a conducting solvent from a polyvinyl alcohol layer containing a carbon image.

As a specific example of this process illustrated in FIG. 3, a sheet of direct positive film bearing a positive silver image was desiccated in a pattern cor esponding to that of the silver image, simply by passing the sheet through a commercial copying device of the type used by thermal recording and illustrated schematically in FIG. 1. film was then placed on a grounded plate, support side down and charged under a negat ve corona. It was then developed with a commercial xerographic developer of the cascade type and the positive image was transferred by simple pressure to a sheet of ordinary bond paper.

Example 1 A 12 percent solution of poly(vinyl hydrogen phthalate) in acetone was coated on a whirl coater at 860 rpm. onto map overlay tracin paper. This was run through a standard thermal exposing machine, coated side in contact with printed material. The paper, polymer side up, was then charged positively under a corona discharge and cascade developed with Haloid Lithmaster Developer having negatively charged toner particles. A very legible image was obtained, wrong-reading from the polymer side, right-readingthrough the paper. Paper coated in this way could be used several months after preparation. It is believed that the principle of tms system is based on moisture retention by the polymer and such theory is supported by the observation that somewhat greater maximum developed density is obtained when the process is run at 20 percent RH. rather than at 50 percent RH.

- Example 2 A coating similar to that in Example 1 was exposed in the standard thermal exposing machine polymer side away from the copy. On charging and development, as illustrated in HG. 2, a right-reading copy from the'polymer side was obtained.

The I Example 3 A coating similar to that in Example 1 was run through a standard thermal exposing machine three times to give better developed density. It was then charged and developed as in Example 1. Good density in exposed areas was achieved. This example shows that the recording is cumulative, which property can be put to good advantage in some cases.

Example 4 A print was made using a coating of cellulose acetate phthalate by the method of Example 1, but with three passes through a standard thermal exposing machine. This was satisfactory but more hydrophilic polymerspoly(vinyl alcohol), gelatin-do not retain the conductivity image very long after heating and do not give a legible print, unless charged and toned immediately. Thus the invention requires materials which are conducting but which become sufficiently non-conducting upon heating, to store a charge.

Example 5 A polymeric acetal, containing 0.7 percent by weight carboxyl group, was coated from percent solution in ammonia-methanol. After processin" in the manner of Example 1 a good print was obtained. That loss of conductivity due to decomposition of ammonium carboxylate was involved was demonstrated by coating the same polymer in acid form, out of acetone-methanol. Mottled prints with high background density and no image were obtained with the latter coatings. Carboxyl-containing polymers with higher percent carboxyl generally were too conductive when coated as the ammonium salt. Nevertheless this illustrates that conversion of ionic to nonionic compounds can provide a form of thermal sensitivity useful with the present invention.

Example 6 A sheet of 1 mil thick waxed paper was exposed and developed as in Example 1. Legible hnages resulted. Starting with wax paper on which the wax is somewhat thicker and more uniform, and then twisting it so as to introduce imperfections and then exposing, charging and developing it as in Example 1, gave some evidence of image, but not as good as the thinner wax coatings. It is felt that imperfections in the coating of wax prevent it from being a good insulator. When the wax is fused, as in the image areas, it forms a continuous insulating film, capable of maintaining an electrostatic image. Since wax paper with interstices in the wax is difiicult to produce and keep uniformly, such systems are less preferable than the other examples, but this example 6 is given to illustrate that such physical recording is possible.

Example 7 A sheet of map overlay tracing paper was coated as in Example 1 with a solution of percent Vinylite AYAC poiy(vinyl acetate)in methyl isobutyl ketone. After drying, the pa er side was moistened with methyl isobutyl ltetone and allowed to dry (1-2 minutes) to the touch. The coating was then put polymer side towards the printed copy and exposed in the standard thermal exposing machine. The tracing paper was charged negatively under corona discharge and developed with a magnetic brush with iron fillings and carbon pigmented Piccolastic Record Resin (Pennsylvania Industrial Chemical Corp). A fair copy of the original was obtained, wrong-reading from the polymer side, right'reading through the tracing paper. The presence of solvent in this coating undoubtedly deteriorates its insulating properties, which are restored when the sample is heated in the exposed areas.

Example 8 A dope similar to the one in Example 7 was prepared, except that the solvent was 98 percent methyl isobutyl 6 ketonc, 2 percent of the relatively high boiling cyclohexanone. This was coated as in Example 7. Fifteen minutes later, it was exposed in the standard thermal exposing machine without solvent rewetting, polymer side towards copy, and charged and developed, polymer side up. A fair copy was obtained.

Example 9 A coating solution containing 10% Pliolite S-SB styrenebutadiene resin, and 1% AgI was prepared by mixing 10 ml. of a 15% solution of Pliolite S-SB in cyclohexanone with 0.5 ml. of an acetone solution containing 30% AgI and 9% KI and diluting to 15 ml. with acetone. Hand coatings were prepared on a coating block using map overlay paper as the support, and these were air dried. A coating thickness of about 0.5 mil or greater was desired. In separate experiments, coatings of this type were found to show an increase of resistivity of l2 orders of magnitude when heated in the standard thermal exposing machine. Since conductivity of these coatings is only very slightly dependent on humidity, there is the possibility that electronic conductivity is involved. To prepare a copy of printed matter, the coated side of the copy paper was placed next to the side containing the printing and exposed in the standard thermal exposing machine. (This is reflex copying which yields a wrong reading copy, that is, the copy must be read through the support.) The exposed coated side of the copy paper was then charged under a positive corona and cascaded with negative polarity toner particles carried by Haloid Developer Type 10, the exposed or letter areas picking up toner, due to a residual charge in these areas and little or no charge in the background areas. The image was fixed by rte-exposing the toned copy in the standard thermal exposing machine. The copies obtained by this technique also showed some background toner picleup which could not be completely eliminated.

Example 10 Coatings made from 10% Pliolite S-SB solutions containing up to 3% Agl gave facsimile copies when treated in the same manner as discussed in the preceding paragraph. These coatings exhibited the same properties as was described for coatings containing 1% Agi.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. The process of recording an energy pattern which comprises impinging said energy pattern on a sheet of material which increases in electric charge storing ability when heated by said energy, then uniformly applying electrostatic charge to the surface of said sheet which charge accumulates more in the areas heated by said energy than in the non-heated areas and xerographically toning said surface while a substantially greater charge remains on the heated areas than on the non-heated areas, whereby toner is deposited in an imagewise distribution on said surface.

2. The process accoording to claim 1 in which the pattern is one of heat applied by direct contact between said sheet and a patternwise heated member.

3. The process according to claim 1 in which a document with characters which absorb radiant heat, is placed in contact with said sheet and subjected to radiant heating to heat said characters and thus impinge a heat pattern on said sheet by conduction.

4. The process of thermoxerographic recording which comprises imagewise heating a sheet of material which increases in electric charge storing ability when heated, then uniformly applying electrostatic charge to the surface of said sheet which charge accumulates more in the heated areas than in the non-heated areas and xerographically 3,161 sea toning said surface while a substantially greater charge remains on the heated areas than on the non-heated areas, whereby toner is deposited in an imagewise distribution on said surface.

5. The process according to claim 4 in which said sheet is placed in contact with a document having heat-absorbing characters thereon and said imagewise heat is produced by passing said sheet and document under a source of infrared radiation.

6. The process according to claim 4 in which said sheet is conducting due to the presence of moisture and said heating drives out moisture from said sheet.

7. The process according to claim 4 in which said sheet is conducting due to the presence of an organic solvent and said heating drives out the solvent.

8. The process according to claim 4 in which said sheet is an organic compound which cross links to a high resistance polymer under the action of heat and said heating increases the cross linking of said compound.

9. The process according to claim 4 in which said sheet 20 References tilted in the file or" this patent UNlTED STATES PATENTS 2,476,145 Gwyn et al July 12, 1949 2,593,758 Murray Apr. 11, 1950 2,551,582 Carlson May 8, 1951 2,616,961 Groak Nov. 4, 1952 2,740,184 Thomas Apr. 3, 1956 2,793,959 Moncrief-Yeates July 9, 1957 2,847,330 Toulmin Aug. 12, 1958 2,881,470 Berthold et a1. Apr. 14, 1959 2,982,647 Carlson et a1 May 2, 1961 3,681,699 Guiko Mar. 19, 1963 3,100,702 Rauner et a1 Aug. 13, 1963 3,110,621 Doggett et a1 Nov. 12, 1963 

1. THE PROCESS OF RECORDING AN ENERGY PATTERN WHICH COMPRISES IMPINGING SAID ENERGY PATTERN ON A SHEET OF MATERIAL WHICH INCREASES IN ELECTRIC CHARGE STORING ABILITY WHEN HEATED BY SAID ENERGY, THEN UNIFORMLY APPLYING ELECTROSTATIC CHARGE TO THE SURFACE OF SAID SHEET WHICH CHARGE ACCUMULATES MORE IN THE AREAS HEATED BY SAID ENERGY THAN IN THE NON-HEATED AREAS AND XEROGRAPHICALLY TONING ON THE HEATED AREAS THAN ON THE NON-HEATED AREAS, WHEREBY TONER IS DEPOSITED IN AN IMAGEWISE DISSTRIBUTION ON SAID SURFACE. 